The present invention relates to a melting and casting furnace particularly, but not exclusively, of the vacuum induction type.
Vacuum induction melting and casting furnaces are well known in the art. In this type of furnace melting is carried out under conditions of reduced pressure and heating is achieved by means of an induction coil. There are many different types of design. The simplest design is a single chamber system with a turntable in which the melting unit within the chamber is movable to pour into removable moulds situated on a turntable. With such a design, the chamber has to be opened for loading and unloading after each melt. An improvement of the single chamber design is achieved with a 2-chamber system separated by vacuum gate valves in which tundishes move between the 2 chambers to direct the melt from the melting unit into the mould and the mould assembly/array can be rotated by a turntable. The advantage of this design is that the melting chamber can still be closed and maintained under reduced pressure for a complete melt cycle. In another system a large mould chamber is isolated by vacuum gate valves with movable mould cars so that again the melting chamber can be maintained under reduced pressure for a complete melt cycle. In another design the entire mould chamber and turntable can be moved and the two chambers are separated by a vacuum gate valve so that one or more moulding chambers can be brought into position to receive the melt from the melting chamber.
In all of the aforementioned arrangements the melting chamber is fixed or else can move horizontally, but the melting unit is tiltable inside the melting chamber so that the melt can be poured either directly into the mould or more usually into a tundish which directs the melt to an assembly or array of moulds in turn. It will be understood that in the present specification, the term tundish is used to denote a collecting and pouring device of a type well known in the art and movable so as to convey and discharge molten metal, the term including any suitable device of this type, for example a launder or the like.
A different design of vacuum induction chamber is one in which the melt chamber and the melting unit are tilted together, the melt chamber is coupled to a mould chamber through a rotary vacuum seal and a movable launder which is usually resident in the mould chamber is fed through the rotary vacuum seal to receive the melt and direct the flow into the assembly or array of moulds. This system, although offering a degree of flexibility, results in a relatively complex furnace design and limits control over molten metal flow and filtration resulting in excessive turbulence with increased possibility of refractory inclusion. It is difficult to obtain satisfactory rotary vacuum seals, with the result that the problems can occur in attaining acceptable purity in cast ingots for certain types of materials. In addition rotary seals are complex, difficult to fabricate and maintain.
Perhaps the main problem with all aforementioned designs is that each system is not flexible enough to cope with the various casting processes required. Thus, if more that one type of casting process is required during a specific melting cycle then the whole furnace has to stop production for a different mould chamber to be coupled to the furnace. This introduces long shut-downs and the possibility of atmospheric pollution which can result in the contamination of the melt and the resultant cast product.
There has been proposed a two chamber system separated by a vacuum gate valve consisting of a horizontal melting chamber and mould chamber. In this concept the furnace change is allowed by utilising of two furnace inserts each being mounted on a swivel door. This is alleged to improve casting continuity and the casting of different kinds of melt. However, this arrangement does not solve the basic problem of allowing different types of casting processes without interrupting the complete operation and cycling of the furnace.